Power amplifiers for wireless (e.g., radio frequency or RF) communications devices may use transistors which require a DC power feed that isolates RF energy. While gallium nitride (GaN) technology has extended transistor power amplifier RF operating bandwidth capabilities, bias feed networks may provide an impediment to such capabilities in some applications.
More particularly, for low frequency and broad-band amplifiers, DC power feeds are typically injected with an inductor, or bias choke, which passes DC but blocks RF energy. Yet, as signal bandwidths are extended, the reactance (inductance) of the bias feed network may cause problems, including non-quasi stable distortion (memory-like) effects. This distortion may not be correctable with memory-less (LUT-based) pre-distortion linearization techniques, for example.
Historically, for high frequency and narrow band amplifiers, the DC power feed is achieved using a quarter-wave shorted line. This presents an “open” impedance to the PA at RF frequencies, and a low-inductance short at baseband frequencies.
Despite the existence of such configurations, further enhancements for power amplifier feed networks may be desired in certain applications.